Lubricity

[MolaKule]

Originally Posted By: Michael_P
Lubricity. That has to be one of the most over used and mis used words in the world of motor oil.


So true.

Lubricity originally meant the capacity of a substance to reduce friction or wear, is not a material property, and cannot be measured directly.

Two fluids can have the same viscosity, but in tests, one may result in a smaller wear scar than the other.

So a reduction in friction and wear is primarily the result of the additive technology.

I discourage my students from the using the term, "Lubricity" because 1) it is often misunderstood, 2) is used too broadly, 3) may mean anything in today's vernacular, and 3) is not narrowly defined enough to be useful.

 

[mjoekingz28]

Ok Molakule, would 'slicker' be preferred?


I felt a reduction in friction as the dipstick would glide down the dipstick tube more easily and when wiping it (to check level) it binded less and slid easier. At least that is how I think what happened to start this thread.



So we'll instate slicker as the new industry term instead of misusing lubrious!

 

[mjoekingz28]

Lubricious......


There we go, I looked it up......

Although one of the terms is ....???

 

[MolaKule]

Originally Posted By: mjoekingz28
Ok Molakule, would 'slicker' be preferred?


I felt a reduction in friction as the dipstick would glide down the dipstick tube more easily and when wiping it (to check level) it binded less and slid easier. At least that is how I think what happened to start this thread.



So we'll instate slicker as the new industry term instead of misusing lubrious!


Nope. Neither is meaningful or accurate.

 

[DWC28]

Lubricity is one of my favorite subjects and I agree with MolaKule. Isaac Newton many years ago measured coefficient of friction of fluids. He found they all were proportional to viscosity in hydrodynamic lubrication. The thinner the oil the more lubricity if you do not go into boundary. The problem for most of us is we assume viscosity stays the same, that is at 100C, no shear and room pressure. At high pressures PAO are thinner than mineral oils (lower alpha)so better lubricity. At low temperatures high VI oils are thicker than low VI oils so better lubricity. At high temperature low VI oils are better... until you reach boundary. So to quantify lubricity you need to know viscosity at operating temperature, pressure and shear, and be in hydrodynamic conditions. I like the Stribeck curve.

 

[DWC28]

Originally Posted By: DWC28
Lubricity is one of my favorite subjects and I agree with MolaKule. Isaac Newton many years ago measured coefficient of friction of fluids. He found they all were proportional to viscosity in hydrodynamic lubrication. The thinner the oil the more lubricity if you do not go into boundary. The problem for most of us is we assume viscosity stays the same, that is at 100C, no shear and room pressure. At high pressures PAO are thinner than mineral oils (lower alpha)so better lubricity. At low temperatures high VI oils are thicker than low VI oils so better lubricity. At high temperature low VI oils are better... until you reach boundary. So to quantify lubricity you need to know viscosity at operating temperature, pressure and shear, and be in hydrodynamic conditions. I like the Stribeck curve.


high VI oils are thinner..

 

[Ducked]

Originally Posted By: Shannow


Back in the days before FMs were recognised, they knew that these types of oils were desirable, and were usually obtained from animal fats and castor oil type bases.

Steam train oils for bearings and link pins still have animal fats (tallowates) in them.


I read somewhere that marine steam engines used (use?) rapeseed oil a lot. Something to do with resisting wash-off, IIRC.

 

[Txchl33]

Rough bunch Joe.

 

[kschachn]

Originally Posted By: MolaKule
I discourage my students from the using the term, "Lubricity" because 1) it is often misunderstood, 2) is used too broadly, 3) may mean anything in today's vernacular, and 3) is not narrowly defined enough to be useful.


I find it is most often used as a vague marketing term for various additives, when they wish to make it sound like they're are saying something but actually not.

"Increases lubricity".... Just how is that being measured?

 

[Ohle_Manezzini]

Slippery in dipstick oils...